It has become common practice to contain groups of parallel extending electrical wires within extruded U-shaped channels, or ducts. However, electricians, seeking to make electrical connections between one or more of such wires and a point outside the duct, have run into the rather exasperating and time consuming problem of making an opening in the sides of the duct. Shears, for example, can readily make cuts which are perpendicular to the top edge of the duct, but it is extremely awkward to make a cut parallel to the top edge with shears. It is therefore desirable to provide a breakaway line along the bottom of each side of the duct and parallel to the top edge. With such a line, the electrician can make two parallel cuts with shears and then snap out a section of the side of the duct along the breakaway line.